We propose to investigate the mechanisms by which phi105 prophage DNA is integrated and excised from the chromosome of its host, Bacillus subtillis. The integrative form of phi105 DNA i.e., whether it is a linear or circular molecule, will be determined by analyzing the composition of the prophage-bacterial DNA junctions. These junctions will be cleaved from lysogen DNA by restriction endonucleases and their composition, with respect to segments of the phage genome from around the att site(s), will be determined by their ability to hybridize with radioactively labeled restriction fragments. The excision process will be investigated by following the fate of the prophage-bacterial DNA junctions in induced lysogens. Such a study will enable us to analyze the extent of in situ prophage replication which occurs during phi105 induction and to determine if prophage excision is related to other processes such as DNA packaging. We also plan to continue our investigations of the genetic regulation of phi105 lysogenization and the process of transformation-mediated phi105 prophage induction.